Preprints  

The `Likhall´ zircon bed helps to constrain the timing of increased meteorite bombardment of the Earth, during the Ordovician period. It is important to understand the timing of this meteorite bombardment when attempting to correlate it with biodiversity changes during the Ordovician period. Calibrating a good age for the ´Likhall´ bed is however challenging and benefited in this study from advances in sample preparation.

The mollusc Arctica islandica can survive for hundreds of years and its annual growth captures environmental conditions, so each shell provides a detailed climatic record. Dating is essential for sample selection, but radiocarbon and crossdating are time-consuming and costly. As an alternative, amino acid geochronology was investigated in the three aragonitic layers forming the shells. This study confirms the value of AAG as a method for rangefinder dating Quaternary A. islandica shells.

We demonstrate a machine learning method to estimate the temperature changes of the earth's crust over time. The method respects physical laws and conditions imposed by users. By using observed rock cooling ages as constraints, the method can be used to estimate the tectonic and landscape evolution of the earth. We show the applications of the method using a synthetic rock uplift model in 1D and an evolution model of a real mountain range in 3D.

The work presented here focusses on understanding the nature and lifespan of the Delamerian Orogeny (mountain belt). The results obtained support the hypothesised nature of the long-lived Delamerian Orogeny. The orogen has potential for Cu-Au deposits and the results contribute to the fundamental understanding of the region that will assist in exploring for mineralisation. The aims have been achieved through ⁴⁰Ar/³⁹Ar dating of important structures within the rock units of the orogen.

We describe a new method of reconstructing the long-term, pre-observational frequency and/or intensity of wildfires in forested landscapes using trace concentrations of the noble gases helium and neon that are formed in soil mineral grains by cosmic-ray bombardment of the Earth's surface.

Radiometric dating methods, involving laser-ablation as sample introduction, require robust calibrations to reference materials with similar ablation properties to the analysed samples. In the case of the Rubidium-Strontium dating method, calibrations are often conducted to a nano-powder with different ablation characteristics than crystalline minerals. We describe the limitations of this approach and recommend an alternative calibration method, involving natural minerals.

Developing models that relate stratigraphic position to time are important because they allow the rock record to be understood in terms of absolute time, allowing global comparisons. In this study we developed a novel method for developing these models (called age-depth models) that uses two different types of chronologic information, dated rocks, and records of variations in earths orbit (astrochronology). The resulting models are very precise which can improve understanding of past climates.

Chemical abrasion (CA) is a technique that reduces or eliminates the effects of Pb-loss in zircon U-Pb geochronology. However, CA has yet to be applied to large-n detrital zircon (DZ) analyses. We show that CA does not negatively impact or systematically bias U-Pb dates and improves concordance, precision, and accuracy. When applied to DZ samples prior to laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), CA improves the resolution of DZ age populations.

Acid leaching is used to remove radiation-damaged portions of zircon crystals prior to U-Pb dating to improve the accuracy of datasets. We test how the temperature and duration of acid leaching affects geochronological and geochemical outcomes. We build a framework that relates radiation damage, zircon solubility, and Pb loss that will ultimately help researchers to tailor their acid leaching approach to different zircon samples.

Decay of U to Pb in the mineral baddeleyite is used for precisely dating mafic rocks, but some daughter Pb atoms can be ejected out of the crystal, resulting in an age that appears too young. Atom Probe Tomography was used to map the distribution of U and Pb atoms in 3 dimensions within a baddeleyite crystal and estimate the average distance that Pb atoms are displaced by decay of U. This allows us to correct the measured age on a baddeleyite crystal knowing its size and shape.

Sedimentary provenance utilizes the composition of sedimentary rocks to investigate the sources of sediment and the geologic processes controlling it. Common techniques struggle to track mafic igneous and metamorphic rock sources, yet rutile forms in these rock types. We use rutile from ancient sedimentary rocks in Türkiye to present a new workflow for integrating rutile U-Pb ages and chemical composition into an accurate sedimentary provenance reconstruction.

This study tested the application of single-grain feldspar luminescence for dating and reconstructing sediment dynamics of an extreme mass movement event in the Himalayan Mountain range. Our analysis revealed that feldspar signals can be used to estimate the age range of the deposits if the youngest subpopulation from a sample is retrieved. The absence of clear spatial relationships with our bleaching proxies suggests that sediments were transported under extremely limited light exposure.

We investigate the relationship between damage trails from uranium fission in apatite and the etched tracks measured with an optical microscope. We aim to understand sampling biases and to improve etching, selection and measurement protocols. The track orientation and length, apatite and track etch rate, and effective etch time co-determine whether a track is suitable for measurement. Reliable data are attainable because the specific sample properties have but a limited effect on these factors.

We conducted a preliminary study using a synchrotron light source to produce elemental maps, including oxidation states, with spatial resolution <1 µm of individual K-feldspar grains previously used in luminescence dating. The elemental fingerprint that characterised grains with a signal suitable for infrared-radiofluorescence dating had high concentrations of K, Pb and Ba and low proportions of Fe and Ca. In contrast, grains with high Fe and Ca levels yielded an unexpected curve shape.

As a result of increasing precision and accuracy in geochronology, interpreting complicated age spectra has become increasingly important, since individual mineral ages often do not directly date the actual geologic process of interest. Here we propose a method for estimating the age of eruption or deposition of a set of minerals dated by the U-Pb system which, in contrast to previous approaches, remains accurate even when the dated minerals have experienced loss of the daughter product Pb.

Reliable chronologies lie at the base of paleoclimatological reconstructions. When working with marine sediment core, the most common dating tool for recent sediments is radiocarbon, but this requires calibration to convert to calendar ages. This calibration requires knowledge of the marine radiocarbon reservoir age and this is known to vary in space and time. In this study we provide 92 new radiocarbon measurements to improve our knowledge of the reservoir age around Greenland.

The mineral zircon is widely used to determine the age of rocks based on the radioactive decay of U to Pb, but the measured U-Pb date can be too young if the zircon loses Pb. We present a new method for estimating the distribution of apparent Pb loss by mathematical convolution. Applying this approach to 10 samples illustrates contrasting patterns of apparent Pb loss. This study highlights the importance of quantifying Pb loss to better understand its potential effects on zircon U-Pb dates.

The carbonate wall deposits of the Trou du Renard Cave (France) were dated using a multimethod approach: U-Th dating by bulk dissolution of samples and ICPMS, U-Th dating by laser ablation ICPMS imaging and radiocarbon dating. The sample compositions were studied to ensure that they can give reliable ages. Ages ranging from 187.9 ± 5.3 ka and 1.4 ± 0.1 ka were found. This approach should make it possible to establish more robust chronologies of archaeological caves.

Volcanic ash layers are a common tool to synchronize records of past climate, and their estimated age relies on external dating methods. Here, we show that the chemical composition of the well-known, 12000 year-old Vedde Ash is indistinguishable with several other ash layers in Iceland that are ~1000 years younger. Therefore, chemical composition alone cannot be used to identify the Vedde Ash in sedimentary records.

The Great Unconformity represents an enormous amount of time lost from the sedimentary record. Its origin is debated, in part, due to different approaches used to interpret zircon (U–Th)/He ages. This thermochronometric system is ideal for this problem because the temperature sensitivity varies according to radiation damage. Here we explore the uncertainty associated with the radiation damage model and show how this limits our ability to resolve the origin of the Great Unconformity.

We proposed a new non-destructive mineralogical methodology on inframilimetric grains that allows to quantify the hematite and goethite content and hematite/goethite ratio of grains prior to (U-Th)/He geochronological analysis. (U-Th)/He data performed on different aliquots with different acquisition time shows no remarkable differences in age, opening a new way to investigate the (U-Th)/He data evolution in supergene lateritic duricrusts.

Paleomagnetic data from Cascade Lake (Brooks Range, Alaska) extend the radiometric-based age model of the sedimentary sequence extending back 21 kyr. Correlated ages based on prominent features in paleomagnetic secular variations (PSV) diverge from the radiometric ages in the upper 1.6 m, by up to about 2000 years at around 4 ka. Four late Holocene cryptotephra in this section support the PSV chronology and suggest the influence of hard water or aged organic material.

Prehistoric volcanic eruptions are often dated by wiggle matching series of radiocarbon ages on tree rings to standard calibration curves, ignoring potential contamination by 'old' carbon given off by the volcano. We modeled the effects of low amounts of contamination on wiggle match dates for the 10th century Changbaishan eruption and found evidence of contamination in all. We propose a new protocol to identify the presence of contamination, and provide more secure dates for major eruptions.

The timing and duration of fluid activity within a gold deposit enables a greater understanding of how the deposit evolved and thus help future mineral exploration. This research uses high resolution dating methods to unravel the overprinting fluid activity at the Martabe gold field in Sumatra. Methods outline in this report can be applied to deposits globally.

Potassium-based geochronology, including the ⁴⁰Ar/³⁹Ar and K-Ar methods, provides critical constraints on the timing and duration of many events and processes in earth history. These methods assume that a key parameter, the fraction of potassium with a mass of 40, does not vary in some relevant materials. Some recent work has identified some variability in these materials. This work examines the effects of this variability on calculated K-Ar and ⁴⁰Ar/³⁹Ar ages.